Cathode ray tube



June 24, 1969 D, H. PRITCHARD CATHODE RAY TUBE Filed Dec. 27, 1961 U.S. Cl. 313-69 United States Patent O 3,452,233 CATHODE RAY TUBE Dalton Harold Pritchard, Princeton, NJ., assignor to Radio Corporation of America, a corporation of Delaware Filed Dec. 27, 1961, Ser. No. 162,322 Int. Cl. H015 29/46, 31/12, 31/20 14 Claims This invention relates to cathode ray tubes of the type utilizing differential penetration of a luminescent screen by a plurality of different Velocity electron beams to obtain plural color image re-creation, and particularly to the mutual registering of the plurality of rasters produced by the plurality of electron beams.

One type of cathode ray tube referred to above includes a luminescent screen having three different phosphors which are disposed in superimposed layers, each of which is capable of emitting, for example,` a different one of the three primary colors, red, green, and blue. The tube further includes three electron guns, each adapted vto project a different velocity electron beam through a cornmon deflection field and onto the luminescent screen. Electrons ofthe lowest velocity beam excite the first phosphor layer to produce light of a first color; electrons of the medium velocity beam penetrate the first layer and excite the second layer to produce light of a second color; and electrons of the highest velocity beam penetrate both the first and second layers and excite the third layer to produce light of a third color. Proper current intensity modulation of the three beams enables production of any desired mixture of these three colors.

In tubes of the type described above, unless preventive or corrective means are provided, the three rasters produced by the three electron beams are of different-size. This is because the three beams, being of different velocity,are deflected different amounts by the common deflection field.

Substantially equal size and coincident red, green, and blue rasters can be obtained by differentially shielding the beams from portions of the common deflection field. Individual magnetic tubular shields are disposed around the two lower velocity beams and extend different distances in the common defiection field. Thus, the two lower velocity beams, which .in the absence of lthe magnetic tubular shields would be defiected the greater amounts by the common field, are subjected to different selected fractions of the field and thereby are deflectedthe same amount as the highest velocity, unshielded, beam.

In such tubes, magnetic tubular shields serve their intendedA purpose to prevent creation of greatly differentsize rasters and thus contribute greatly to raster registers. However, their presence in the common deflection fields causes distortions of the fields, which although of relatively small magnitude,` are complex in nature. The distortions, in turn, affect the different Ibeams differently and thus cause slight misregister of the three rasters. n

It is therefore an object of this invention to provide a plural beam cathode ray-tube of the type having a magnetic tubular beam shield, which tube operates with improved register of the plurality of rasters produced thereby. v p

According to one feature of my invention, a cathode ray tube includes one or more magnetic tubular beam shields, each of which has a substantially higher magnetic reluctance in the longitudinal direction than it `does laterally, or circumferentially. Each shield may comprise a plurality of magnetic elements so arranged that the shield is magnetically discontinuous in `the axial direction. For example, each shield may comprise a plurality of spaced (c g., axially spaced), coaxial, magnetic rings. The number of, length of, diameter of, and spacing beice tween, the rings of any one tubular shield is such that the desired amount of shielding is provided to produce the desired size of raster scanned by the beam associated with that shield.

According to another feature of my invention, in a plural beam cathode ray tube having a plurality of such shields one for each beam, the rings of each shield are preferably of such size and number and so spaced that the plurality of tubular shields are substantially equal to each other in overall length.

Accordin-g to still another feature of the invention, such equal length shields are preferably disposed sideby-side and are coextensive with each other.

In the drawings:

FIG. 1 is a side elevation view partly in section and with parts broken away of a cathode ray tube incorporating tubular magnetic shields embodying the invention; FIGS. 2, 3, and 4 are transverse sections of the cathode ray tube of FIG. 1 taken, respectively, along lines 2-2, 3 3, and 4 4;

FIG. 5 is a perspective of a portion of the cathode ray tube of FIG. l; and

FIG. 6 is a longitudinal section view of another form of tubular magnetic shield embodying the invention.

FIG. 1 illustrates a cathode ray tube 8 comprising an evacuated envelope including a neck section 10, a faceplate 12, and an interconnecting funnel section 14. Disposed within the neck 10 is an electron assembly 15 comprising, for example, three electron guns 16, 17, and 18 positioned side-by-side in a delta triangular arrangement symmetrically about the longitudinal axis of the gun assembly 15. In FIG. 1 gun 17 is hidden behind gun 16. The electron guns 16, 17, and 18 are respectively adapted to project lower, medium, and higher velocity electron beams through a common deflection zone 19 and toward the faceplate 12. For the purpose of brevity and clarity, the terms L beam, M beam, and H beam will be hereinafter used to refer respectively to the lowest velocity beam (and its gun 16), the medium velocity beam (and its gun 17), and the highest velocity beam (and its gun 18).

A luminescent screen 20' on the faceplate 12 includes three layers 22, 24, and 26 of dierent phosphors, each of which luminesceses in a different one of the three primary colors, red, green, and blue. In the drawings the phosphor layers 22, 24, and 26 are representatively shown as continuous. However, the layers may be provided in other suitable forms such as a multiplicity of particles each of wlllich includes superimposed coatings of different phosp ors. The tube 8 is operated so that electrons of the L beam will excite the first phosphor layer 26 to produce light of a first primary color; electrons of the M vbeam will penetrate the first phosphor layer 26 and excite the second phosphor layer 24 to produce light of a second primary color; and

I electrons of the H -beam will penetrate both the first and y second phosphor layers 26 and 24 and excite the third phosphor layer 22 to produce light of a third primary color. A metal backing layer 27 of, eg., aluminum, is disposed on the phosphor layer 26 as is known in the art. If desired, the screen 20 may include nonluminescent separator layers between the phosphor layers to improve the operational characteristics of the screen.

v As an adjunct to the electron tube 8, a magnetic deflection yoke 28 is provided which closely encircles the envelope of the tube. The yoke 28, when suitably energized, is adapted to create horizontal and vertical magnetic deflection fields inthe deflection zone 19 to cause the three sepavrate beams of the electron guns 16, 17, and 18 to scan a desired raster or pattern on the luminescent screen 20. A shield 29 is provided at the rear of the yoke 28 to reduce the rearward extent of the fringe portion of the deflection elds formed by the yoke.

Each of the electron guns 16, 17, and 18 comprises a plurality of coaxial tubular electrodes. Each gun includes a tubular cathode 30` having an end wall which is coated with a suitable electron emissive material. Each cathode 30 is insulatingly mounted within a centrally apertured control grid cup 32. Disposed coaxially beyond the control grid cups 32, in the order named, are for each gun, a centrally apertured screen grid cup 34, a tubular focusing electrode 36, and a tubular anode 38.

The anodes 38 are mounted on a cylindrical convergence cage 40 which is electrically common to all three of the electron guns 16, 17, and 18. The convergence cage 40 comprises a cup which has an end Wall 42 and which is closed at its open end with an end plate 43. Both the end wall 42 and the end plate 43 are provided with apertures 44, 45, and 46 which are coaxial respectively with the three electron guns 16, 17, and 18.

The cathodes 30, control grids 32, screen grids 34, and focusing electrodes 36 of the electron guns 16, 17, and 18 are individually connected to different ones of a plurality of lead-in conductors 50 which are sealed through the vacuum envelope in a stem base 52. Thus, each of these electrodes can be energized independently of the others to provide electron beams of different velocities which are independently focused in the region of the screen 20.

The convergence cage 40 is provided with a plurality of spring snubbers 54 which bear outwardly against the neck of the envelope. An electrically conductive coating 56 disposed on the internal surface of the envelope extends over the funnel -14 and into the neck 10 a distance sufcient to make contact with the snubbers 54. The coating '56 also extends into electrical contact With the metal backing layer 27 of the luminescent screen 20. Terminal means, such as is illustrated schematically by the arrow 58, is provided for applying a suitable electrical potential to the coating electrode 56, the anodes 38, and the luminescent screen 20 The electrodes of each of the electron guns 16, 17, and 18 are maintained in xed spaced coaxial relationship in a well-known manner such as by mounting them on three glass rods 59 which extend along the guns. Each of the electrodes 32, 34, 36, and 38 of each of the three guns is iixed to the glass rods in a manner similar to that illustrated for the focusing electrodes 36 in FIG. 2. As shown in FIG. 2, the electrode 36 of gun 18 is attached to a central arcuate section of a strap 60 whose ends are embedded into two of the glass rods 59. The electrodes of guns 16 and 17 are mounted by similar straps 61 and 62 respectively to different pairs of the glass rods 59. The strap 60 on the electrode 36 of the H gun 18 may be made of magnetic material for a purpose hereinafter described. Further details of the mounting ofthe electron guns 1'6, 17, and `18 have been omitted from the drawing for purposes of clarity.

Because the three electron guns 16, 17, and 18 are noncoaxial with respect to the tube 8, each gun being mounted slightly off the longitudinal axis of the tube, both static and dynamic convergence of the three beams is provided to compensate for this off axis mounting. Such convergence is in accordance with known color television receiver techniques.

t Approximate convergence may be provided by mounting each gun at a small angle with respect to the longitudinal axis of the tube 8 so that the three electron beams, when undeected, are caused to converge approximately at a common point near the center of the luminescent screen 20. The angle which each gun makes with the tube axis is determined by the dimensions of the tube. In cathode ray tubes of the type described having a tube length of about 19 to 25 inches, this angle is in the order of 11.

Dynamic convergence may be provided as shown in FIG. 3. A separate pair of pole pieces 64 are disposed on 4 opposite sides'of each'beam within the convergence cage 40. The pole pieces 64 are axially spaced back from the end plate 43 to reduce interference by the fringe of the deflection fields with the elds generated by pole pieces 64.

Associated with each pair of pole pieces 64 is a separate electromagnet 66 disposed externally of the tube envelope adjacent to the ends of the pole pieces. More refined arrangements, such as those incorporating a pair of electromagnetic windings in place of the single winding 66, are known in the art but for the `sake of brevity and clarity are not herein detailed. A Y-shaped magnetic shield 68 is disposed within the convergence cage for shielding each beam from the convergence elds of the other beams.

'Energization of the coils of the electromagnets 66 will impart to the respective electron beams a small radial directional component of deflection toward or away from the longitudinal axis of the tube 8. A varying current synchronized with, and related to, the amount of scanning deection of the three beams isapplied to each electromagnet 66 to provide the desired dynamic convergence of the three beams. Also, in accordance with known techniques, all three beams are brought to a precise static convergence at the center of the luminescent screen 20 by means provided for adjusting the lateral position of one of the electron beams. This isv accomplished by a magnetic iield established in the path of the H beam by a permanent magnet assembly 69 (best seen in FIG. 2). In order to help shape the eld of the magnet assembly 69 in the path of the H beam, the mounting strap L60 may in some instances be rnade of magnetic material. The eld produced by the magnet 1assernbly 69 is transverse to the direction of the magnetic eld es-tablished between the pole pieces 64 (FIG. 43) for gthe H beam. This permits a lateral adjustment of the position of one of the three electron beams |(viz, the beam produced by the electron gun 18 in the illustrated embodiment) in a direction which is normal to -the radial adjustment of this same beam as provided by the convergence pole pieces 64.

If desired, the poles of the magnet assembly 69 (FIG. 2) may be dynamically energized to provide an additional means contributing to the shaping of the H beam raster for the purpose of registering this raster with the rasters of the L and M beams.

A pair of thin-plate permanent ring magnets 70 and 71 (FIG. 1) :are disposed around the tube neck 10 behind the magnet assembly 69. The ring magnets 70 and 71 are individually rotatable relative to each other to provide a desired intensity magnetic iield transversely of the neck 10. This serves to laterally position the three beams as a unit so that they have an optimum relationship with the deflection iields in the deflection zone 19.

The L beam gun 16 and M beam gun 17 (FIG. 2) are provided withor have associated therewith--tubular magnetic shield members (i.e., magnetic shunts) 76 and 78 (FIGS. l, 4 and 5) respectively, each of which comprises a plurality of spaced coaxial rings of magnetic material mounted on a support. The tubular array of rings of each shield 76 and 78 is disposed coaxially with its respective gun 16 and 17. The tubular shields 76 and 78 extend from and are so positioned with respect to the electron gun apparatus that they are disposed within the deection zone 19. They may be mounted on the end plate 43. f

Deflection eld enhancer elements 80 and 81 (FIGS. l, 4 and 5) of magnetic material are disposed on opposite sides of the H beam path. Therenhancer elements 80 and 81 are attached to the end plate 43 and extend along the Hv beam path into the deflection zone 19. The enhancer elements 80 and 81 are preferably tubular members having a rectangular cross section as illustrated and are disposed with their sides parallel to the horizontal and vertical directions of deflection and with their adjacent sides" opposite each other. However, other cross sectional' shapes-such as U-shaped rectangular channel members can be used. The purpose and advantages of the field enhancers 80 and 81 are more fully described hereinafter.

The electron gun apparatus is angularly oriented about the longitudinal axis of the tube 8 relative to the luminescent screen and to the deflection yoke 28 so that the electron gun 18 producing the unshielded H beam is disposed in the central plane which is perpendicular to the scan produced by the higher frequency one of the two orthogonal deflection fields. According to present day practices in home television receivers the unshielded H beam would be disposed in the central vertical plane of the tube 8. Such an orientation has proved to reduce objectionable raster distortion.

The L beam shield 76 comprises a plurality, e.g. five, of coaxial rings 82 of magnetic material which are axially spaced from each other. The rings 82 are mounted on a tubular support 84 of nonmagnetic material and are thus maintained in their desired mutually spaced relationship. The support 84 is fixed to the end plate 43.

The M beam shield 78 comprises a plurality, e.g. four, of coaxial rings 86 of magnetic material which are axially spaced from each other. The rings 86 are mounted in fixed spaced relationship on a nonmagnetic tubular support 88 which is also fixed to the end plate 43.

The cumulative axial length of the magnetc rings 82 of the L beam shield 76 is greater than that of the magnetic rings 86 of the M beam shield 78. In the embodiment illustrated in FIGS. 1, 4 and 5, this differential cumulative length relationship results not only from the fact that there may be more of the L beam shield rings 82 than there are of the M beam shield rings 86, but also because each of the rings 82 may be longer than are the individual rings 86, and because the spacing between the rings 82 is less than is the spacing between the rings 86.

By virtue of the different cumulative lengths of the magnetic rings of the shields 76 and 78 and their disposition in the deflection zone 19, the L beam and the M beam are shielded from the deflection field over different portions of their travel therethrough. The L and M beams are thus subjected to the deflection field for a shorter period of time than they would be in the absence of the shields 76 and 78. By properly relating the cumulative ring lengths of the shields 76 and 78 to the relative beam velocities and to the shape and length of the magnetic deflection field, the L and M beams are subjected to the deflection field for specific time durations which will result in their being deflected substantially the same amount as the unshielded H beam.

Because the shields 76 and 78 comprise spaced shielding elements, i.e., the rings 82 and 86, which are spaced or distributed along a given length support, these shields are termed distributed shields or distributed shunts. The descriptive term distributed is in contrast to prior art single-piece solid tubular shields.

Because there is appreciable spacing between the rings 86 of the M beam shield 78, vthe 4M beam is deflected somewhat as it passes along the length of the shield. Because of this deflection, the M beam shield 78 must be made larger in diameter than the L beam shield 76 in order to prevent the deflected M beam from striking the shield elements.

The M beam shield is made larger in diameter than the L beam shield for the further purpose of symmetrizing the field distortion which is caused by the shields 76 and 78 and which the unshielded H beam encounters. Since the M beam shield comprises less cumulative axial length of magnetic material than does the L beam shield 76, it would ordinarily cause less distortion of the deflection fields. However, its larger diameter compensates for its smaller cumulative length so that the distortions caused by the shields 76 and 78 are more nearly equal and thus produce an overall substantially symmetrized distortion.

In order to -obtain the desired amount of shielding by the M beam shield 78, its two center (or intermediate) rings 86 may be selectively axially positioned along the support member 88 so as to dispose them in a stronger or weaker portion of the deflection field (i.e. the rings 86 -need not be uniformly spaced from each other). Such selective positioning of the rings 86 serves as a trim adjustment for the magnitude of the magnetic shunting which is provided by the -M beam shield 78.

The distributed shields 76 and 78 are actually constituted by the magnetic rings themselves. The support members 84 and 86 provide no magnetic shielding but serve as a support for the rings 82 and 86. For this reason the supports for the rings 82 and 86 need not take the form of a tube but may, for example, comprise one or more rods or other means out of the beam paths to which the rings can be attached 4and maintained in their desired space relationship.

Referring to FIG. 6, a distributed shield 90 comprising an alternative embodiment .of the invention is illustrated. The shield 90 comprises a first plurality of axially spaced coaxial magnetic rings 92 and a second plurality of axially spaced coaxial magnetic rings 94. The rings 92 are mounted on the outside surface of a nonmagnetic support tube 96, while the rings 94 are mounted on the inside surface of the support tube 96. The rings 92 and 94 are so relatively axially positioned that they overlap each other.

Axial magnetic discontinuity is provided in the distributed shields 76 and 78 of FIG. 5 by virtue of the axial spacing of the adjacent rings. Axial magnetic discontinuity is provided in the distribu-ted shield 90 of FIG. 6 by virtue of the radial spacing between the overlapped portions of the rings 92 and 94. Axial discontinuity is one way of obtaining the feature of differential magnetic reluctance within a given shield wherein the reluctance in the axial direction is greater than that in the lateral (circumferential) direction. As described below, this feature is believed to be responsible for reducing or eliminating the various deflection field distortions, one of which is manifest as a skewing of the unshielded H beam raster.

In a skewing of the type in question, the skewed raster is distorted from an otherwise rectangular shape to that of a parallelogram with horizontal top and -bottom boundaries and nonvertical side boundaries. This type of distortion is ldifficult to correct by conventional techniques, such as `by the applying of special signal voltages to the dynamic convergence magnets 66. A horizontal raster shape adjustment is needed; but the convergence system I64-66 provides displacement of the H beam only in the vertical direction.

A skewed H beam raster is believed to result from nonuniform and nonsymmetrical relationships of a tubular beam shield with respect to -the deflection field in which the shield is disposed. For example, the typical deflection field is of nonuniform intensity along the axis of the cathode ray tube, increasing from zero to a maximum and then decreasing back to zero. A nonsymmetrical relationship results from the fact that magnetic beam shields are usually disposed in the edge or fringe portions of the deflection field. Thus, the field lines intercepted by the shields are not perpendicular at the axis of the shiel-d tubes. Because of the nonuniform intensity of the deflection field and the angular relationship of the field lines with the shield tubes, axial magnetic currents are induced in the shields, if the shields are of solid one-piece elements according to prior art design. These axial currents cause such shields to act as magnets, and the shields, in turn, create field lines externally of the shield which include an axial component.

If the tubular shields are characterized by a high reluctance in the axial direction relative to their reluctance in the lateral or circumferential direction, then the axial magnetic currents referred to above are reduced or effectively prevented from occurring in the shields. Distributed shields are effectively magnetically nonconductive in the axial direction. Distributed shields comprising a plurality of spaced magnetic rings have a relatively higher axial reluctance due to their magnetic discontinuities in the axial direction, and therefore substantially vprevent the creation of harmful axial magnetic currents.

I do not intend that my invention Ibe predicated upon, or Iotherwise limited by, any particular theory as to the cause of the skewed H beam raster. However, it 'is believed that the presence of the above-described axial eld formation is the cause of such skewing. Whether this is so or not, .the fact remains that the use of distributed shields according to my invention has reduced skewing .of the H beam raster where it has been encountered. Distributed shields have also effectively reduced deflection field distortions which cause an undesired, nonun'iform expanding or compression of the corners of 4one or more of the H beam or M beam rasters.

|Distributed shields such as the shields 76 and 78 have been successfully used in a three-gun, twenty-three inch, rectangular, 92 cathode ray tube in which the cathode of the H beam gun is operated at -7 kilovolts, the M beam gun cathode at ground, the L lbeam gun cathode at +6 kilovolts, and the luminescent screen at +19 kilovolts. Such tubes have incorporated either a single distributed L beam shield 76 together with a solid onepiece M lbeam shield or both a distributed L beam shield 76 and a distributed M beam shield 78. Substantially improved results have been obtained even where only the L beam shield is provided in distributed form. Of course, in the optimum arrangement, both the L beam and M beam shields are distributed. In such a system fthe L beam shield 76 has been provided either as: (a) twenty 1/16-inch-long rings 82 spaced `0.005 linch apart, (b) ten 1/s-inch-long rings 82 spaced im inch apart, or (c) five 1Much-long rings 82 spaced 1/32 inch apart. The M 'beam shield has been provided as four 1/lg-inch-long rings I86 distributed in spaced relationship .over 1% inches. 'Such shields made from a combination of alloys sold commercially and designated Netic and Conetic have been found suitable. In one embodiment each shield ring 82 or 86 has consisted of a four mil thick Netic ring snugly fitted over a four mil thick Conetic ring. Another commercially available alloy which has been found to be suitable is that sold by Allegany Ludlum Co. and identified as alloy No. 4750.

In a cathode ray tube incorporating a plurality of distributed shields, the shieds are, according to a perferred practice of the invention, made equal in length and coextensive. Such a construction is illustrated in FIG. l,

wherein the tubular distributed shields 76 and 78 are coextensive along the axis of the tube. This construction provides the advantage of subjecting one of the shielded beams to a portion of the deflection field which has substantially the same raster shaping characteristics as does the portion of the deflection field to which the other shielded beam is subjected.

This advantage stems from the fact that a deection field is actually an integration of a plurality of sub-fields which have different raster shaping characteristics such as coma, astigmatism, trapezodial, pincushion, and barrel.

If unequal length tubular shields are disposed in the integrated deflection field, the longer of the two shields may completely shield one beam path from one of the sub-fields, whereas the shorter of the two shields will permit another beam to be partly subjected to that same sub-field. Thus the deflection fields to which the two beams are respectively subjected comprise different ratios of the various raster shaping sub-fields. The respecti-ve rasters produced are thus differently shaped. By providing coextensive distributed shields wherein different degrees of shielding are possible with equal length coextensive shields, the respective portions of the integrated defiection field to which the tWo beams are subjected are more nearly identical as to their raster shaping characteristics.

Regarding the functioning of the enhancers and 81, if a pair of enhancers are disposed in both the horizontal and vertical fields, they will enhance the strength of the deflection field in one direction, e.g., horizontal, and decrease the strength of the field in the perpendicular direction, e.g., vertical in the space between the enhancers which is the region of the electron beam path with which they are associated. If the horizontal and vertical deflection fields are not coextensive and the er1-4 enhancers are disposed in only one of the fields, they will affect only that field.

Since enhancers are placed adjacent a particular beam path and primarily associated therewith (e,g., enhancers 80 and 81 for the H beam), they primarily affect the deflectionfield only locally for the particular beam associated therewith. Enhancers act as magnetic conductors which are placed in the gap between a pair of deflection coils and thus decrease the reluctance of the deflection field fiux path in the localized area occupied by the enhancers.

The pair of H beam enhancers 80 and 81, being aligned in a horizontal plane, conduct the horizontally directed fiux lines producing the vertical H beam deflection and thus enhance the vertical deflection of the H beam and thereby expand the H beam raster vertically.

In following the path of least reluctance, the horizontal flux lines of the vertical defiection eld are bent toward and pass through the enhancers 80 and 81. The enhancers may be thought of as gathering the ux lines from surrounding areas concentrating them. Since the enhancers are arranged serially in the direction of the fiux lines, the flux in 4the area between the enhancers 80 and 81 is concentrated and provides a stronger vertical deection field of the H beam than would otherwise exist without the enhancers. This serves to expand the height of the H beam raster. At the same time, the vertical fiux lines of the horizontal -deection field are bent toward and pass through the enhancers 80 and 81. Since the enhancers are arranged in parallel in the direction of the horizontal deflection fiux lines, they gather flux which would otherwise pass between the enhancers, and thereby the enhancers lower the ux concentration in that area and provide a weaker horizontal deection field for the H beam. This results in a horizontal contraction of the H beam raster. The vertical expansion and horizontal contraction of the resulting H beam raster are additive in effecting a change of the aspect ratio of the raster.

What is claimed is:

1. A cathode ray tube having a deflection zone and comprising:

(a) a luminescent screen;

(b) an electron gun for projecting an electron beam along a path through said deflection zone toward said screen; and

(c) a plurality of axially spaced, coaxial, magnetic shield rings disposed in said defiection zone and each surrounding said path.

2. A cathode ray tube comprising:

(a) a luminescent scrceen;

(b) an electron gunfor projecting an electron beam along a path toward said screen; and y (c) a defiection zone in the path of said beam between said gun and said screen for the establishing of magnetic deflection fields therein for scanning said beam in a raster over said screen',

(d) said gun including a magnetic tubular shield comprising a plurality of axially spaced, coaxial, magnetic rings each surrounding said path in said defiection zone.

3. A cathode ray tube having a defiection zone and comprising:

(a) a luminescent screen;

(b) an electron gun for projecting an electron beam along a path through said deflection zone toward said screen; and v (c) a magnetic tubular shield disposed in said deflection zone and surrounding said path;

(d) said tubular shield having a greater magnetic reluctance in its axial direction than in its circumferential direction. ,p y

4. A cathode ray tube having a deflection zone and comprising:

(a) a luminescent screen;

(b) an electron gun for projecting an electron beam along a path through said deflection zone toward said screen; l j

(c) a magnetic tubular shield comprising a plurality of axially spaced, coaxial, magnetic rings disposed in said deflection zone and each surrounding said path; and

(d) a non-magnetic member extending along said tubular shield and supporting said rings.

5. A cathode ray tube having a deflection zone and comprising:

(a) a luminescent screen;

(b) a plurality of electron guns for projecting a plurality of electron beams along a plurality of separate paths through said deilection zone toward said screen; and

(c) a plurality of magnetic tubular shields disposed in said deflection zone, each surrounding a different one of said beam paths;

(d) one of said tubular shields comprising a plurality of spaced, coaxial, magnetic rings.

`6. A cathode ray tube comprising:

(a) a luminescent screen;

(b) a plurality of electron guns for projecting a plurality of electron beams along a plurality of separate paths toward said screen;

(c) a dellection zone in the paths of said beams between said screen and said guns for the establishing of magnetic deflection fields therein for scanning said beams in a raster over said screen; and

(d) a plurality of magnetic tubular shields disposed in said deflection zone; each surrounding a different one of said beam paths (e) one of said tubular shields comprising a plurality of spaced, coaxial, magnetic rings.

7. A cathode ray tube having a deflection zone and comprising:

(a) a luminescent screen;

(b) a plurality of electron guns for projecting a plurality of electron beams along a plurality of separate paths through said deflection zone toward said screen; and

(c) a plurality of magnetic tubular shields disposed in said deflection zone;

(d) each of said tubular shields comprising a plurality of spaced, coaxial, magnetic rings surrounding a different one of said beam paths; and

(e) the magnetic rings of one of said tubular shields having a greater cumulative length along its associated beam path than the rings of another one of said tubular shields.

8. A cathode ray tube having a deflection zone and comprising:

(a) a luminescent screen;

(b) a plurality of electron guns for projecting a plurality of electron beams along a plurality of separate paths through said deflection zone toward said screen; and

(c) a plurality of magnetic tubular shields disposed in said deflection zone;

(d) each of said tubular shields comprising a plurality of spaced, coaxial, magnetic rings surrounding a different one of said beam paths; and

(e) one of said tubular shields having fewer rings than another of said tubular shields with each of the rings of said one shield being axially shorter than, and spaced -farther apart than, those of said another shield.

9. A cathode ray comprising:

(a) a luminescent screen; and

(b) a plurality of electron guns for projecting a plurality of electron beams along a plurality of separate paths through said deflection zone toward said screen;

`(c) each of said guns including a magnetic tubular shield comprising a plurality of spaced, coaxial, magnetic rings surrounding its beam path in said deflection zone;

(d) the tubular shields of said guns being of equallength and axially coextensive; and

(e) the magnetic rings of one of said tubular shields having a greater cumulative length along its beam path than the rings of another one of said tubular shields.

10. A cathode ray tube having a deflection zone and comprising:

(a) a luminescent screen;

(b) a plurality of electron guns for projecting a plurality of electron beams along a plurality of ibeam paths through said deflection zone toward said screen;

(c) a plurality of nonmagnetic tubular support members, each surrounding a different one of said beam paths; and

(d) a plurality of equal-length, axially coextensive, magnetic tubular shields disposed in said deflection zone;

(e) each of said tubular shields comprising a plurality of axially spaced, coaxial, magnetic rings co-axially mounted on a different one of said nonmagnetic tubular support members;

(f) the rings of one of said tubular shields being larger in diameter, fewer in number, axially shorter, and spaced axially further apart than the rings of another one of said tubular shields.

11. A cathode ray tube having a deflection zone for establishing of magnetic raster-scanning deflection fields therein comprising:

(a) a luminescent screen;

(b) an electron gun for projecting an electron beam toward said screen along a path through said dellection zone; and

(c) magnetic shield means disposed in said deflection zone and comprising a plurality of axially spaced elements of magnetic material spaced along said path for shielding said path from portions of said fields.

12. A cathode ray tube having a deflection zone for the establishing of magnetic deflection iields therein comprising:

(a) a luminescent screen;

(b) an electron gun for projecting an electron Ibeam toward said screen along 4a path through said dellection zone; and

(c) an elongated magnetic shield disposed in said deflection zone and surrounding said path and being axially magetically discontinuous;

(d) said shield shielding said path from portions of said fields.

.13. A cathode ray tube having a deflection zone for the establishing of magnetic raster-scanning deflection fields therein comprising:

(a) a luminescent screen;

(b) a plurality of electron guns for projecting a plurality of electron beams toward said screen along a plurality of separate paths through said deflection zone; and

(c) a plurality of elongated magnetic shields disposed in said deflection zone;

(d) each of said shields extending along and magnetitube having a deflection zone and 11 L callyl shielding a diierent one of said paths from portions of said fields; j

(e) one of said shields having magnetic discontinuities spaced longitudinally therealong.

14. A cathode ray tube having a deection zone and comprising: f

(a) aluminescent screen;

(b)` three electron guns for projecting three electron beams of different velocities along three separate paths through said deilection zone toward said screen; and

(c) two elongated magnetic shields disposed in said deection zone, each surrounding .a different one of said beam paths;

(d) each of said shields comprising a l plural spaced, coaxial, magneticrings; l,

(e) the cumulative lengths of he magnetic rings of said two shields along the associatedvhearn paths .'being different. l t

IReferences* .Cited UNITED STATES PATENTS 2,727,171 1 2/1955 De Gier 1 315-85 X 2,790,920 4/1957 Todd v; 313-84 2,898,491 8/1959 Pearce 1 313-821 10 HERMAN'KARL SAALBACH, Primary Examiner.

t f y v y 3 15 174-35; 313-82, 83, 326; 335-210 

1. A CATHODE RAY TUBE HAVING A DEFLECTION ZONE AND COMPRISING: (A) A LUMINESCENT SCREEN; (B) AN ELECTRON GUN FOR PROJECTING AN ELECTRON BEAM ALONG A PATH THROUGH SAID DEFLECTION ZONE TOWARD SAID SCREEN; AND (C) A PLURALTY OF AXIALLY SPACED, COAXIAL, MAGNETIC SHIELD RINGS DISPOSED IN SAID DEFLECTION ZONE AND EACH SURROUNDING SAID PATH. 